Ohhh no, I realised one of my snails has lost its two long antannas its shorter now, also once I saw one of my fantail fish sucked up the flesh of one of my snails so I kept it away with my fish net and it fled, so does anyone know how I can keep my snails out of harm? So worried when I sleep the fantail might attack the snail... it occurs in the evening the attacks normally during the day it's not much to worry so I go to bed worrying.

Some goldfish , not all, will find it hard to resist the wiggling antennae from snails that can look like delicious worms. Many goldfish will leave the snails alone , but once in a while you will get a goldfish that just love to go after the snails. I think your only solution is probably to either separate the fantail or the snails, since they obviously can't live together.

Yes I will have to rehome my snails because the purpose of them in the tank is for the benefit of my goldfish but unfortunately one of my fantail is mistaking it's soft flesh as food and antannae as worms just like what @Nabi claimed...